I have been using iPhone 3.0.1 with Zimbra 5.0.18 without any problems. All calendars from 2 servers are visible, up to date and I could add new an appointment from the phone.

When I upgraded to 3.1 version, I cannot any more add an appointment to the default calendar (Zimbra Calendar). The default calendar is visible as a calendar, but it it is not visible in the list where you can add an appointment. I can add an appointment to all other calendars I have created,

Propably the reason why the default calendars do not show up in the list, when adding new appointment, is that these seems to be READ ONLY.
I cannot change any appointment which are in the default calendar. All calendars I have created in Zimbra I can edit in the iPhone.

Which one to correct iPhone or Zimbra?

-- Timo

SOLVED:

I deleted the caldav accounts in iPhone and recreated them. After recreation the all calendars are R/W and working OK.